Nobody would fault you for bringing a Swiss Minigun C1ST to a knife-fight. Recognised by the Guinness Book of World Records as the smallest functional revolver on the planet, this diminutive firearm makes Derringers look like Desert Eagles.
The C1ST Miniature Revolver is a small batch specialty firearm produced by the Swiss Minigun company of Switzerland. It measures 5.5cm long, 3.5cm tall, 1cm wide, and weighs just 19.8 grams. It fires equally minuscule ammo, 2.34mm rimfire cartridges, which also hold the record for world's smallest ammunition. In fact, each round produces less than a joule of energy, travels at a pokey 400 feet per second and impacts with .71 foot pounds of energy, according to the manufacturer.
To put that in perspective, the .41 Rimfire cartridge normally used in Derringers produce 52 foot-pounds force (71 Joules). So unless you stuck the muzzle right against someone's eyeball, firing this weapon -- even at point blank range -- will do little but piss off your quarry.
For as harmless as this weapon is, it's still a weapon and one that is banned from import to the United States and the UK and Australia. It is so small that it doesn't meet the minimum size requirements for a sporting revolver set by the ATF. The C1ST's easy concealment also works to its disadvantage in the eyes of the law.
Swiss Minigun has been making the C1ST since 2005 in very small batches, with only about 300 of the tiny sidearms having been produced in that time. These firearms are not cheap, mind you. The double action revolvers retail for $US5,500 for the base silver on a wood handle model up to $US20,000 for one made of 24-carat gold with a diamond-encrusted handle. [Wikipedia - How Stuff Works - Swiss Minigun - Buzzfeed]